Lithographic apparatus and device manufacturing method

ABSTRACT

A lithographic projection apparatus is disclosed in which a space between the projection system and the substrate is filled with a liquid. An edge seal member at least partly surrounds the substrate or other object on a substrate table to prevent liquid loss when edge portions of the substrate or other object are, for example, imaged or illuminated.

This is a divisional application of U.S. application Ser. No.10/705,804, Nov. 12, 2003 now U.S. Pat. No. 7,199,858, which claimspriority from European patent applications EP 02257822.3, filed Nov. 12,2002, and EP 03253636.9, filed Jun. 9, 2003, each of which areincorporated herein in their entirety by reference.

FIELD

The present invention relates to immersion lithography.

BACKGROUND

The term “patterning device” as here employed should be broadlyinterpreted as referring to means that can be used to endow an incomingradiation beam with a patterned cross-section, corresponding to apattern that is to be created in a target portion of the substrate; theterm “light valve” can also be used in this context. Generally, the saidpattern will correspond to a particular functional layer in a devicebeing created in the target portion, such as an integrated circuit orother device (see below). Examples of such a patterning device include:

A mask. The concept of a mask is well known in lithography, and itincludes mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. Placementof such a mask in the radiation beam causes selective transmission (inthe case of a transmissive mask) or reflection (in the case of areflective mask) of the radiation impinging on the mask, according tothe pattern on the mask. In the case of a mask, the support structurewill generally be a mask table, which ensures that the mask can be heldat a desired position in the incoming radiation beam, and that it can bemoved relative to the beam if so desired.

A programmable mirror array. One example of such a device is amatrix-addressable surface having a viscoelastic control layer and areflective surface. The basic principle behind such an apparatus is that(for example) addressed areas of the reflective surface reflect incidentlight as diffracted light, whereas unaddressed areas reflect incidentlight as undiffracted light. Using an appropriate filter, the saidundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light behind; in this manner, the beam becomespatterned according to the addressing pattern of the matrix-addressablesurface. An alternative embodiment of a programmable mirror arrayemploys a matrix arrangement of tiny mirrors, each of which can beindividually tilted about an axis by applying a suitable localizedelectric field, or by employing piezoelectric actuation means. Onceagain, the mirrors are matrix-addressable, such that addressed mirrorswill reflect an incoming radiation beam in a different direction tounaddressed mirrors; in this manner, the reflected beam is patternedaccording to the addressing pattern of the matrix-addressable mirrors.The required matrix addressing can be performed using suitableelectronic means. In both of the situations described hereabove, thepatterning device can comprise one or more programmable mirror arrays.More information on mirror arrays as here referred to can be gleaned,for example, from United States patents U.S. Pat. Nos. 5,296,891 and5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096,which are incorporated herein by reference. In the case of aprogrammable mirror array, the said support structure may be embodied asa frame or table, for example, which may be fixed or movable asrequired.

-   -   A programmable LCD array. An example of such a construction is        given in United States patent U.S. Pat. No. 5,229,872, which is        incorporated herein by reference. As above, the support        structure in this case may be embodied as a frame or table, for        example, which may be fixed or movable as required.

For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table;-however, the general principles discussed in such instancesshould be seen in the broader context of the patterning device ashereabove set forth.

Lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs). In such a case, the patterningdevice may generate a circuit pattern corresponding to an individuallayer of the IC, and this pattern can be imaged onto a target portion(e.g. comprising one or more dies) on a substrate (silicon wafer) thathas been coated with a layer of radiation-sensitive material (resist).In general, a single wafer will contain a whole network of adjacenttarget portions that are successively irradiated via the projectionsystem, one at a time. In current apparatus, employing patterning by amask on a mask table, a distinction can be made between two differenttypes of machine. In one type of lithographic projection apparatus, eachtarget portion is irradiated by exposing the entire mask pattern ontothe target portion at one time; such an apparatus is commonly referredto as a wafer stepper. In an alternative apparatus—commonly referred toas a step-and-scan apparatus—each target portion is irradiated byprogressively scanning the mask pattern under the projection beam in agiven reference direction (the “scanning” direction) while synchronouslyscanning the substrate table parallel or anti-parallel to thisdirection; since, in general, the projection system will have amagnification factor M (generally <1), the speed V at which thesubstrate table is scanned will be a factor M times that at which themask table is scanned. More information with regard to lithographicdevices as here described can be gleaned, for example, from UnitedStates patent U.S. Pat. No. 6,046,792, incorporated herein by reference.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g. in a mask) is imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (resist).Prior to this imaging step, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake andmeasurement/inspection of the imaged features. This array of proceduresis used as a basis to pattern an individual layer of a device, e.g. anIC. Such a patterned layer may then undergo various processes such asetching, ion-implantation (doping), metallization, oxidation,chemo-mechanical polishing, etc., all intended to finish off anindividual layer. If several layers are required, then the wholeprocedure, or a variant thereof, will have to be repeated for each newlayer. Eventually, an array of devices will be present on the substrate(wafer). These devices are then separated from one another by atechnique such as dicing or sawing, whence the individual devices can bemounted on a carrier, connected to pins, etc. Further informationregarding such processes can be obtained, for example, from the book“Microchip Fabrication: A Practical Guide to Semiconductor Processing”,Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4, incorporated herein by reference.

For the sake of simplicity, the projection system may hereinafter bereferred to as the “lens”; however, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The radiation system may also include componentsoperating according to any of these design types for directing, shapingor controlling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens”.Further, the lithographic apparatus maybe of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Dual stage lithographicapparatus are described, for example, in United States patent U.S. Pat.No. 5,969,441 and PCT patent application WO 98/40791, incorporatedherein by reference.

It has been proposed to immerse the substrate in a lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final opticalelement of the projection lens and the substrate. The point of this isto enable imaging of smaller features because the exposure radiationwill have a shorter wavelength in the liquid than in air or in a vacuum.(The effect of the liquid may also be regarded as increasing theeffective NA of the system).

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, United States patent U.S. Pat. No.4,509,852, hereby incorporated in its entirety by reference) may meanthat there is a large body of liquid that must be accelerated during ascanning exposure. This may require additional or more powerful motorsand turbulence in the liquid may lead to undesirable and unpredictableeffects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection lens and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application WO 99/49504, hereby incorporatedin its entirety by reference. As illustrated in FIGS. 22 and 23, liquidis supplied by at least one inlet IN onto the substrate, preferablyalong the direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet OUT after having passedunder the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 23 shows thearrangement schematically in which liquid is supplied via inlet IN andis taken up on the other side of the element by outlet OUT which isconnected to a low pressure source. In the illustration of FIG. 22 theliquid is supplied along the direction of movement of the substraterelative to the final element, though this does not need to be the case.Various orientations and numbers of in- and out-lets positioned aroundthe final element are possible, one example is illustrated in FIG. 23 inwhich four sets of an inlet with an outlet on either side are providedin a regular pattern around the final element.

SUMMARY

Difficulties in large loss of liquid from the liquid supply system canarise with the system described above and any other systems that provideliquid on only a localized area of the substrate and between theprojection system and the substrate when the localized area crosses overan edge of the substrate or other object.

Accordingly, it maybe advantageous to provide, for example, alithographic projection apparatus in which liquid loss from the supplysystem is minimized during passage over an edge portion of the substrateor other object.

According to an aspect, there is provided a lithographic projectionapparatus comprising:

-   -   a support structure configured to hold a patterning device, the        patterning device configured to pattern a beam of radiation        according to a desired pattern;    -   a projection system configured to project the patterned beam        onto a target portion of a substrate;    -   a substrate table configured to hold the substrate, said        substrate table comprising an edge seal member configured to at        least partly surround an edge of at least one of said substrate        and an object positioned on said substrate table and to provide        a primary surface facing said projection system substantially        co-planar with a primary surface of the said at least one of        said substrate and said object; and    -   a liquid supply system configured to provide a liquid, through        which said beam is to be projected, in a space between said        projection system and said at least one of said substrate and        said object, wherein said liquid supply system provides liquid        to a localized area of at least one of said object, said edge        seal member and said substrate.

Where applied to a substrate, the edge seal member surrounds a positionon the substrate table where, in use, the substrate is to be placed,e.g., surrounding the chuck or pimple table on which the substrate isheld. In this way the substrate can be positioned closely adjacent tothe edge of the edge seal member such that as an edge of the substratemoves under the projection system there is no sudden loss of liquid fromthe space because there is no large gap for the liquid to flow through.The edge seal member may be an integral part of the substrate table ormay be moveably mounted relative to the remainder of the substratetable. In the latter case, it can be arranged such that the gap betweenthe edge seal member and the substrate can be varied and/or the heightof the primary surface of the edge seal member can be varied toaccommodate variations in substrate height or thickness, i.e., to ensurethat the primary surface of the edge seal member is substantiallycoplanar with the primary surface of the substrate. The above may alsobe applied to an object on the substrate table such as a sensor, e.g., aprojection beam sensor.

In an embodiment, the substrate table comprises a gap seal memberconfigured to abut or at least partly overlap, in the direction of theoptical axis, both the edge seal member and said at least one of saidsubstrate and said object. For example, in this way the gap between theedge seal member and a substrate (or an object), which is due to thesize mismatch between the inner edge of the edge seal member and theouter edge of the substrate or object (which is necessary to accommodateslight variations in the diameter of the substrate or object), can becovered by the gap seal member. This further reduces the amount ofliquid loss into the gap between the edge seal member and the substrateor object. In an embodiment, the gap seal member is configured to be incontact with the primary surfaces, thereby spanning the gap between theedge seal member and said at least one of said substrate and saidobject.

If the gap seal member has inner and outer edges, at least one of theedges maybe tapered such that the thickness of the gap seal memberfacing away from the edge seal member or said at least one of saidsubstrate and said object decreases towards the edge of the gap sealmember. This helps the liquid supply system move smoothly over the gapbetween the substrate or object and the edge seal member.

A way to hold the gap seal member removably in place is to provide thesubstrate table with a vacuum port in the primary surface of said edgeseal member.

Another way to minimise the amount of liquid which escapes into the gapbetween the edge seal member and the substrate or object is to providethe substrate table with a hydrophobic layer facing edge portions ofsaid edge seal member and the substrate or object on an opposite side ofthe edge seal member and the substrate or object to the projectionsystem. Such a hydrophobic layer may be any material which exhibitshydrophobic properties, for example Teflon, silicon rubber or otherplastics materials. Inorganic coatings are generally desired becausethey have better radiation resistance than organic coatings. In anembodiment, the liquid has a contact angle of greater than 90° with thehydrophobic layer. This reduces the chances of liquid seeping into thegap.

According to an aspect, there is provided a lithographic projectionapparatus comprising:

-   -   a support structure configured to hold a patterning device, the        patterning device configured to pattern a beam of radiation        according to a desired pattern;    -   a projection system configured to project the patterned beam        onto a target portion of a substrate;    -   a substrate table configured to hold the substrate, said        substrate table comprising:    -   an edge seal member configured to at least partly surround an        edge of at least one of said substrate and an object positioned        on said substrate table, and    -   a further edge seal member configured to extend across the gap        between said edge seal member and said at least one of said        substrate and said object and to be in contact with said at        least one of said substrate and said object; and    -   a liquid supply system configured to provide a liquid, through        which said beam is to be projected, in a space between said        projection system and said at least one of said substrate and        said object.

In this way the gap between the edge seal member and the substrate orobject is closed off so that there is no gap between the edge sealmember and the substrate or object through which liquid from the liquidsupply system can pass. This is particularly so if the further edge sealmember is flexible in which case a better seal between the further edgeseal member and the substrate or object is achievable.

In an embodiment, the flexible further edge seal member is attached tothe edge seal member and has a port, connected to a vacuum source,adjacent its end distal from said edge seal member, such that onactuation of said vacuum source, said flexible further edge seal memberis deflectable upwards to contact against the substrate or object toform a seal between said flexible further edge seal member and thesubstrate or object due to the force generated by the vacuum sourceacting on the substrate or object. This allows the flexible further edgeseal member to be actuatable to contact with the substrate or object andto be deactuatable so that it falls away from the substrate or object.The application of the vacuum ensures a good seal between the flexiblefurther edge seal member and the substrate or object.

In another embodiment, the flexible further edge seal member is disposedbetween the edge seal member and the substrate or object and with asurface substantially co-planar with the primary surfaces of the edgeseal member and the substrate or object. In this way the gap between theedge seal member and the substrate or object can be sealed such thatonly small amounts of liquid can pass into the gap. In an embodiment,the flexible further edge seal member is shaped to contact the substrateor object on the surface opposite its primary surface and may beeffective to apply a force to the substrate or the object away from thesubstrate table when the substrate or object is held on the substratetable. In the case of the substrate, the flexible further edge sealmember in this way may help in the removal of the substrate from thesubstrate table after exposure of the substrate.

According to an aspect, there is provided a lithographic projectionapparatus comprising:

-   -   a support structure configured to hold a patterning device, the        patterning device configured to pattern a beam of radiation        according to a desired pattern;    -   a projection system configured to project the patterned beam        onto a target portion of a substrate;    -   a substrate table configured to hold the substrate, said        substrate table comprising:    -   an edge seal member configured to at least partly surround an        edge of at least one of said substrate and an object positioned        on said substrate table, and    -   at least one of a vacuum port and a liquid supply port        positioned to provide respectively a vacuum or liquid to the gap        between said edge seal member and said at least one of said        substrate and said object on a side opposite said projection        system;    -   a liquid supply system configured to provide a liquid, through        which said beam is to be projected, in a space between said        projection system and said at least one of said substrate and        said object.

In the case of a liquid supply port, no liquid can find its way into thegap between the edge seal member and the substrate or object from thespace between the projection system and the substrate or object, becausethat gap is already filled with liquid. If the vacuum alternative isused, any liquid which does find its way into that gap will be removedand may be recycled. The provision of vacuum is advantageous when a gasseal member of a liquid supply system is used to keep the liquid in thespace between the projection system and the substrate or object. This isbecause it can not only remove any liquid passing into the gap but alsoany gas from the gas seal member.

Further, there may be provided a channel positioned radially inwardly ofthe vacuum port, the channel being connected to a gas source such thaton actuation of the vacuum a flow of gas radially outwardly from saidchannel toward said vacuum can be established. Such a flow of gas can beused to ensure that any liquid which does reach the non-immersed side ofthe substrate or object is caught in the gas flow and transported awaytowards the vacuum.

According to an aspect, there is provided a lithographic projectionapparatus comprising:

-   -   a support structure configured to hold a patterning device, the        patterning device configured to pattern a beam of radiation        according to a desired pattern;    -   a projection system configured to project the patterned beam        onto a target portion of a substrate;    -   a substrate table configured to hold the substrate, said        substrate table comprising a support surface configured to        support an intermediary plate between said projection system and        at least one of said substrate and an object positioned on said        substrate table and not in contact with said at least one of        said substrate and said object; and    -   a liquid supply system configured to provide a liquid, through        which said beam is to be projected, in a space between said        projection system and said at least one of said substrate and        said object.

In this way an intermediary plate can be used which is of an overallsize larger than the substrate or object so that, for example, duringimaging of edge portions of the substrate or object, the liquid supplysystem is situated at a medial portion of the intermediary plate suchthat no or few problems with loss of liquid through gaps at edges exist.With such a system it is also possible to provide the substrate tablewith a transmission image sensor (TIS) configured to sense a beam andwherein the intermediary plate is positionable between the sensor andsaid projection system. Thus it is possible for the transmission imagesensor to detect a beam under the same conditions that a substrate is tobe imaged. It will therefore be possible to more accurately position thesubstrate table so that the projection beam is correctly focused on thesubstrate.

According to an aspect, there is provided a lithographic apparatuscomprising:

-   -   a support structure configured to hold a patterning device, the        patterning device configured to pattern a beam of radiation        according to a desired pattern;    -   a projection system configured to project the patterned beam        onto a target portion of a substrate;    -   a substrate table configured to hold the substrate; and    -   a liquid supply system configured to provide a liquid, through        which said beam is to be projected, in a space between said        projection system and at least one of said substrate and an        object positioned on said substrate table, wherein a structure        of the liquid supply system extends along at least part of the        boundary of said space between said projection system and said        substrate table and capillaries extend away from said substrate        table and are positioned between said structure and said        projection system.

In this way, a larger gap may be spanned over the edge of the substrateor object before catastrophic liquid loss occurs as capillary actionaids in the liquid spanning gaps.

In an embodiment, the inner coating of the capillary is hydrophobic andthe apparatus comprises an electric device configured to apply apotential difference between said liquid in said space and saidcapillaries. In this way, an even larger gap may be spanned for liquidloss.

According to an aspect, there is provided a device manufacturing methodcomprising:

-   -   providing a liquid in a space between a projection system and at        least one of a substrate and an object positioned on a substrate        table;    -   projecting a patterned beam of radiation, through said liquid,        onto a target portion of the substrate using the projection        system; and

either: providing an edge seal member surrounding at least part of anedge of said at least one of said substrate and said object and with aprimary surface substantially co-planar to a primary surface of said atleast one of said substrate and said object, wherein said liquid isprovided to a localized area of at least one of said substrate, saidobject, and said edge seal member, or

providing an edge seal member at least partly surrounding an edge ofsaid at least one of said substrate and said object and a further edgeseal member extending across the gap between the edge seal member andsaid at least one of said substrate and said object and in contact withsaid least one of said substrate and said object, or

providing an edge seal member at least partly surrounding an edge ofsaid least one of said substrate and said object and providing at leastone of a vacuum or liquid to the gap between the edge seal member andsaid least one of said substrate and said object on a side of said leastone of said substrate and said object opposite to said projectionsystem, or

positioning an intermediary plate in the space between said least one ofsaid substrate and said object and said projection system and not incontact with said least one of said substrate and said object, or

providing a structure extending along at least part of the boundary ofthe space between said projection system and said substrate table andproviding capillaries extending away from the substrate table betweenthe structure and said projection system.

Although specific reference may be made in this text to the use of theapparatus described herein in the manufacture of ICs, it should beexplicitly understood that such an apparatus has many other possibleapplications. For example, it may be employed in the manufacture ofintegrated optical systems, guidance and detection patterns for magneticdomain memories, liquid-crystal display panels, thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “reticle”, “wafer”or “die” in this text should be considered as being replaced by the moregeneral terms “mask”, “substrate” and “target portion”, respectively.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultravioletradiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in which:

FIG. 1 depicts a lithographic projection apparatus according to anembodiment of the invention;

FIG. 2 depicts the liquid reservoir of a first embodiment of theinvention;

FIG. 3 is similar to FIG. 2 showing an edge seal member on the substratetable according to an embodiment of the invention;

FIG. 4 illustrates a second embodiment of the invention;

FIG. 5 illustrates an alternative form of the second embodiment of thepresent invention;

FIG. 6 illustrates a detail of the second embodiment of the presentinvention;

FIGS. 7 a-d illustrate four versions of a third embodiment of thepresent invention;

FIG. 8 a illustrates a first version of a fourth embodiment of thepresent invention;

FIG. 8 b illustrates a second version of the fourth embodiment;

FIG. 8 c illustrates a third version of the fourth embodiment;

FIG. 9 illustrates in detail further aspects of the first version of thefourth embodiment of the present invention;

FIG. 10 illustrates a fifth embodiment of the present invention;

FIG. 11 illustrates a sixth embodiment of the present invention;

FIG. 12 illustrates in plan the substrate and edge seal member of aseventh embodiment of the present invention;

FIG. 13 illustrates a cross section through the seventh embodiment ofthe present invention;

FIG. 14 illustrates a detail of the seventh embodiment of the presentinvention;

FIG. 15 illustrates in detail a further arrangement of the seventhembodiment;

FIG. 16 illustrates an eighth embodiment of the present invention;

FIG. 17 illustrates a ninth embodiment of the present invention;

FIG. 18 illustrates a tenth embodiment of the present invention;

FIG. 19 illustrates an eleventh embodiment of the present invention;

FIG. 20 illustrates a twelfth embodiment of the present invention;

FIG. 21 illustrates a thirteenth embodiment of the present invention;

FIG. 22 illustrates an alternative liquid supply system according to anembodiment of the invention; and

FIG. 23 illustrates, in plan, the system of FIG. 22.

In the Figures, corresponding reference symbols indicate correspondingparts.

DETAILED DESCRIPTION Embodiment 1

FIG. 1 schematically depicts a lithographic projection apparatusaccording to a particular embodiment of the invention. The apparatuscomprises:

-   -   a radiation system Ex, IL, for supplying a projection beam PB of        radiation (e.g. DUV radiation), which in this particular case        also comprises a radiation source LA;    -   a first object table (mask table) MT provided with a mask holder        for holding a mask MA (e.g. a reticle), and connected to first        positioning means for accurately positioning the mask with        respect to item PL;    -   a second object table (substrate table) WT provided with a        substrate holder for holding a substrate W (e.g. a resist-coated        silicon wafer), and connected to second positioning means for        accurately positioning the substrate with respect to item PL;    -   a projection system (“lens”) PL (e.g. a refractive system) for        imaging an irradiated portion of the mask MA onto a target        portion C (e.g. comprising one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive type (e.g. has atransmissive mask). However, in general, it may also be of a reflectivetype, for example (e.g. with a reflective mask). Alternatively, theapparatus may employ another kind of patterning device, such as aprogrammable mirror array of a type as referred to above.

The source LA (e.g. an excimer laser) produces a beam of radiation. Thisbeam is fed into an illumination system (illuminator) IL, eitherdirectly or after having traversed conditioning means, such as a beamexpander Ex, for example. The illuminator IL may comprise adjustingmeans AM for setting the outer and/or inner radial extent (commonlyreferred to as σ-outer and σ-inner, respectively) of the intensitydistribution in the beam. In addition, it will generally comprisevarious other components, such as an integrator IN and a condenser CO.In this way, the beam PB impinging on the mask MA has a desireduniformity and intensity distribution in its cross-section.

It should be noted with regard to FIG. 1 that the source LA may bewithin the housing of the lithographic projection apparatus (as is oftenthe case when the source LA is a mercury lamp, for example), but that itmay also be remote from the lithographic projection apparatus, theradiation beam which it produces being led into the apparatus (e.g. withthe aid of suitable directing mirrors); this latter scenario is oftenthe case when the source LA is an excimer laser. The current inventionand claims encompass both of these scenarios.

The beam PB subsequently intercepts the mask MA, which is held on a masktable MT. Having traversed the mask MA, the beam PB passes through thelens PL, which focuses the beam PB onto a target portion C of thesubstrate W. With the aid of the second positioning means (andinterferometric measuring means IF), the substrate table WT can be movedaccurately, e.g. so as to position different target portions C in thepath of the beam PB. Similarly, the first positioning means can be usedto accurately position the mask MA with respect to the path of the beamPB, e.g. after mechanical retrieval of the mask MA from a mask library,or during a scan. In general, movement of the object tables MT, WT willbe realized with the aid of a long-stroke module (course positioning)and a short-stroke module (fine positioning), which are not explicitlydepicted in FIG. 1. However, in the case of a wafer stepper (as opposedto a step-and-scan apparatus) the mask table MT may just be connected toa short stroke actuator, or may be fixed.

The depicted apparatus can be used in two different modes:

1. In step mode, the mask table MT is kept essentially stationary, andan entire mask image is projected at one time (i.e. a single “flash”)onto a target portion C. The substrate table WT is then shifted in the xand/or y directions so that a different target portion C can beirradiated by the beam PB;

2. In scan mode, essentially the same scenario applies, except that agiven target portion C is not exposed in a single “flash”. Instead, themask table MT is movable in a given direction (the so-called “scandirection”, e.g. the y direction) with a speed v, so that the projectionbeam PB is caused to scan over a mask image; concurrently, the substratetable WT is simultaneously moved in the same or opposite direction at aspeed V=Mv, in which M is the magnification of the lens PL (typically,M=¼ or ⅕). In this manner, a relatively large target portion C can beexposed, without having to compromise on resolution.

FIG. 2 shows a liquid reservoir 10 between the projection system PL andthe substrate W which is positioned on the substrate stage WT. Theliquid reservoir 10 is filled with a liquid 11 having a relatively highrefractive index, e.g. water, provided via inlet/outlet ducts 13. Theliquid has the effect that the radiation of the projection beam is ashorter wavelength in the liquid than in air or in a vacuum, allowingsmaller features to be resolved. It is well known that the resolutionlimit of a projection system is determined, inter alia, by thewavelength of the projection beam and the numerical aperture of thesystem. The presence of the liquid may also be regarded as increasingthe effective numerical aperture. Furthermore, at fixed numericalaperture, the liquid is effective to increase the depth of field.

The reservoir 10 forms, in an embodiment, a contactless seal to thesubstrate W around the image field of the projection system PL so thatthe liquid is confined to fill the space between the substrate's primarysurface, which faces the projection system PL, and the final opticalelement of the projection system PL. The reservoir is formed by a sealmember 12 positioned below and surrounding the final element of theprojection system PL. Thus, the liquid supply system provides liquid ononly a localized area of the substrate. The seal member 12 forms part ofthe liquid supply system for filling the space between the final elementof the projection system PL and the substrate with a liquid. This liquidis brought into the space below the projection system PL and within theseal member 12. The seal member 12 in an embodiment extends a littleabove the bottom element of the projection system PL, and the liquidrises above the final element so that a buffer of liquid is provided.The seal member 12 has an inner periphery that at the upper end closelyconforms to the shape of the projection system PL or the final elementthereof and may, e.g. be round. At the bottom the inner peripheryclosely conforms to the shape of the image field, e.g. rectangular,though this is not necessarily so. The seal member is substantiallystationary in the XY plane relative to the projection system PL thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the seal member and thesurface of the substrate. This seal is desired to be a contactless sealand may be a gas seal.

The liquid 11 is confined in the reservoir 10 by a seal device 16. Asillustrated in FIG. 2, the seal device is a contactless seal i.e. a gasseal. The gas seal is formed by gas, e.g. air or synthetic air, providedunder pressure via inlet 15 to the gap between seal member 12 andsubstrate W and extracted by first outlet 14. The over pressure on thegas inlet 15, vacuum level or under pressure on the first outlet 14 andthe geometry of the gap are arranged so that there is a high-velocitygas flow inwards towards the optical axis of the apparatus that confinesthe liquid 11. As with any seal, some liquid is likely to escape, forexample up the first outlet 14.

FIGS. 22 and 23 also depict a liquid reservoir defined by inlet(s) IN,outlet(s) OUT, the substrate W and the final element of projectionsystem PL. Like the liquid supply system of FIG. 2 the liquid supplysystem illustrated in FIGS. 22 and 23, comprising inlet(s) IN andoutlet(s) OUT, supplies liquid to the primary surface of the substratein a localized area between the final element of the projection systemand the substrate and can suffer from loss of liquid at the substrateedge.

Thus, as used herein for the embodiments, the liquid supply system cancomprise that as described in relation to FIG. 2 and FIGS. 22 and 23.

A problem with the liquid supply arrangement illustrated in FIGS. 2, 22and 23 occurs when imaging edge portions of the substrate W. This isbecause when the substrate W edge is positioned underneath theprojection system PL one of the constraining walls (the substrate W) ofthe liquid supply system (the bottom one as illustrated) is removedthereby allowing immersion liquid to escape. However, the embodimentsdescribed herein can be used with any other type of liquid supplysystem.

FIG. 3 illustrates how the edge portion of a substrate W may be imagedwithout catastrophic loss of immersion liquid from the liquid supplysystem. This is achieved by the provision of a cover plate or edge sealmember 17 on the substrate table WT. The edge seal member 17 has anupper (as illustrated) primary surface substantially co-planar with theupper primary surface of substrate W and is closely adjacent to the edgeof the substrate W so that there is no sudden loss of liquid as the edgeof the substrate moves under the projection system PL. Some liquid lossinto the gap may still occur. Of course there are arrangements in whichthe whole construction illustrated in FIGS. 2 and 3 is positioned upsidedown so that it is the lower surfaces of the edge seal member and thesubstrate which face the projection system and which are substantiallyco-planar. The surfaces are therefore referred to as the primarysurfaces which face the projection system PL rather than upper surfaces.References herein to upper surfaces and lower surfaces may be alsoappropriately considered as references to lower and upper surfacesrespectively in an upside-down configuration.

With this system, the liquid supply system (e.g. reservoir 10) can bepositioned over the edge of the substrate W and can even be movedcompletely off the substrate W. This enables edge portions of thesubstrate W to be imaged.

The edge seal member 17 may form an integral part of the substrate tableWT (as illustrated in FIG. 4 as edge seal member 117) or may betemporarily mounted relative to the remainder of the substrate table bythe use of, for example, vacuum suction or through use ofelectromagnetic forces. In an embodiment, the edge seal member 17 ismoveable relative to the remainder of the substrate table (asillustrated in FIGS. 5 and 6) such that the height above the substratetable WT of the primary surface of the edge seal member 17 may beadjusted such that it is substantially co-planar with the primarysurface of the substrate W. In this way the same edge seal member 17 maybe used for different thicknesses of substrate W (thickness tolerance isabout 25 μm though the embodiment can account for up to about 0.2 mmvariation). The positioning mechanism for the edge seal member 17 may bethrough use of piezoelectric elements or electromagnetism, worm gear,etc. A suitable mechanism is described in relation to the secondembodiment described below.

The edge seal member 17 maybe formed of several individual segments,each of which surrounds a portion of the edge of the substrate W.

Embodiment 2

A second embodiment is illustrated in FIGS. 4 to 6 and is the same orsimilar as the first embodiment except as described below.

In the embodiment of FIGS. 4 and 5 an edge liquid supply system providesliquid to a reservoir 30 via aport 40. The liquid in the reservoir 30 isoptionally the same as the immersion liquid in the liquid supply system.The reservoir 30 is positioned on the opposite side of the substrate Wto the projection system PL and adjacent the edge of the substrate W andthe edge of the edge seal member 17, 117. In FIG. 5, the edge sealmember 17 is comprised of an element which is separate to the substratetable WT whereas in FIG. 4 the edge seal member 117 is provided by anintegral portion of the substrate table WT. As can be seen most clearlyfrom FIG. 4, the substrate W is supported on the substrate table WT by aso-called pimple table 20. The pimple table 20 comprises a plurality ofprojections on which the substrate W rests. The substrate W is held inplace by, e.g., a vacuum source sucking the substrate onto the topsurface of the substrate table WT. With the use of the reservoir 30,when the edge of the substrate W is being imaged, (i.e. when liquid inthe liquid supply system between the projection system PL and thesubstrate W traverses across an edge of the substrate), liquid cannotescape from the liquid supply system into the gap between the edge sealmember 17, 117 and the substrate W because that space is already filledwith liquid.

The mechanism 170 shown in FIG. 5 for moving the edge seal member 17relative to the remainder of the substrate table WT is illustrated indetail in FIG. 6. The reason for moving the edge seal member 17 in thisway is so that its primary surface can be made to be substantiallyco-planar with the primary surface of the substrate W. This allows asmooth movement of the liquid supply system over edge portions of thesubstrate W so that the bottom inner periphery of the liquid supplysystem can be moved to positions partly on the primary surface ofsubstrate W and partly on the primary surface of the edge seal member17.

A level sensor (not illustrated) is used to detect the relative heightsof the primary surfaces of the substrate W and the edge seal member 17.Based on the results of the level sensor, control signals are sent tothe actuator 171 in order to adjust the height of the primary surface ofthe edge seal member 17. A closed loop actuator could also be used forthis purpose.

In an embodiment, the actuator 171 is a rotating motor which rotates ashaft 176. The shaft 176 is connected to a circular disc at the enddistal to the motor 171. The shaft 176 is connected away from the centreof the disc. The disc is located in a circular recess in a wedge portion172. Ball bearings may be used to reduce the amount of friction betweenthe circular disc and the sides of the recess in the wedge portion 172.The motor 171 is held in place by leaf springs 177. On actuation of themotor the wedge portion is driven to the left and right as illustrated(i.e. in the direction of the slope of the wedge portion) because of theexcentre position of the shaft 176 in the disc. The motor is preventedfrom moving in the same direction as the direction of movement of thewedge portion 172 by the springs 177.

As the wedge portion 172 moves left and right as illustrated in FIG. 6,its top surface 175 (which is the surface of the wedge which is slopedin relation to the primary surface of the edge seal member 17) contactsthe bottom sloped surface of a further wedge member 173 which is fixedto the bottom of the edge seal member 17. The edge seal member 17 isprevented from moving in the direction of movement of the wedge member172 so that when the wedge member 172 moves left and right the edge sealmember 17 is lowered and raised respectively. Some biasing of the edgeseal member 17 towards the substrate table WT may be necessary.

Obviously the further wedge member 173 could be replaced by analternative shape, for example a rod positioned perpendicularly to thedirection of movement of the wedge 172. If the coefficient of frictionbetween the wedge member 172 and the further wedge member 173 is greaterthan the tangent of the wedge angle then the actuator 170 isself-braking meaning that no force is required on the wedge member 172to hold it in place. This is advantageous as the system will then bestable when the actuator 171 is not actuated. The accuracy of themechanism 170 is of the order of a few μm.

Especially in the case of the edge seal member 117 being an integralpart of the substrate table WT, a mechanism may be provided to adjustthe height of the substrate W or the member supporting the substrate Wso that the primary surfaces of the edge seal member 17, 117 and thesubstrate can be made substantially co-planar.

Embodiment 3

A third embodiment is illustrated in FIG. 7 and is the same or similaras the first embodiment except as described below.

This embodiment is described in relation to an edge seal member 117which is an integral part of the substrate table WT. However, thisembodiment is equally applicable to an edge seal member 17 which ismovable relative to the substrate table WT. In this embodiment it is notvital however that the edge seal member 17 has an upper surfaceco-planar with the primary surface of the substrate, but this isdesired. A vacuum port 46 connected to a vacuum source is providedunderneath and adjacent edge portions of the edge seal member 117 andthe substrate W on the opposite side of the substrate W to theprojection system PL. In an embodiment, the port 46 is annular andformed by a continuous groove but may be discontinuous i.e. a discretenumber of openings arranged in a circular pattern. In its simplest formthe embodiment may work only with that vacuum supply via port 46.However, the basic idea can be improved by the provision of a substratetable WT as illustrated in detail in FIG. 7 a which illustrates a firstversion of the third embodiment.

A portion 48 of the substrate table WT extends from the edge of the edgeseal portion 117 radially inwardly so that it is positioned below thesubstrate table W on the other side of the substrate W to the projectionsystem PL. Any immersion liquid which leaks through the gap between theportion 48 and the substrate W is attracted towards the vacuum sourcevia port 46. A channel 42 is provided radially inwardly of the vacuumsource also under the substrate W and is connected to a gas source. Thismay be a gas at a pressure greater than atmospheric pressure or it maybe that the channel 42 is simply open to the atmosphere. This creates aflow of gas radially outwardly below the substrate W between the portion48 of substrate table WT below the substrate W and the pimple table 20.(The pimple table 20 has its own vacuum source to hold the substrate inplace.) With this flow of gas any liquid escaping between edge sealmember 117 and the substrate W is pulled towards an annular compartment44 (roughly 3×3 mm in cross section) in fluid connection with the vacuumsource. The compartment 44 is positioned between an annular port 47 opento the gap and the port 46 connected to the vacuum source. Thecompartment helps in establishing uniform flow around the periphery. Thechannel 42 is connected to a continuous annular groove (shown as awidening of the duct). The compartment 44, port 47, and/or the groove ofchannel 42 need not be annular and can be other appropriate shapes orconfigurations.

In one working embodiment, the gap between the portion 48 of substratetable WT and the substrate W is of the order of up to 100 μm (though thegap may not exist i.e. is zero), which prevents a high flow rate ofliquid through the gap due to capillary action. The height of theportion 45 of the substrate table WT between the groove connected tochannel 42 and compartment 44 is such that the distance between thebottom of the substrate W and the top of that portion 45 (indicated asdistance D1 in FIG. 7 a) is typically of the order of 100 μm and ischosen such that a uniform gas flow of in the region of at least 1 m/sis achievable with a pressure loss of less than 0.5 bar. Such anarrangement ensures that only very little, if any, liquid passes throughthe gap D1 and interferes with the pimple table 20. Other values willalso work.

A first version of the third embodiment illustrated in FIG. 7 a maysuffer from deflection of the outer 10 mm or so of the substrate W. Ascan be seen from FIG. 7 a this area is unsupported even though, as saidabove, portion 45 can be extended to underneath the substrate W where itsupports the substrate W. However, at the very outer radius both theweight of the substrate W and the capillary force of liquid between thesubstrate W and portion 48 of the substrate table WT can still deflectthe edge of the substrate W. This may be deleterious. Solutions to thisproblem are illustrated in FIGS. 7 b-d which illustrate second throughfourth versions of the third embodiment.

In the second version illustrated in FIG. 7 b, the portion 48 has atleast one set of burls 348 positioned around and near to the edge of theperiphery of the substrate W (typically in a circular pattern). As theburls 348 are discrete, immersion liquid can still seep between theportion 48 and the substrate W but the weight of the substrate W issupported by the at least one set of burls 348. In an embodiment, theburls 348 have a smaller height than the burls of the pimple table 20which compensates for the difference in the force downwards on thesubstrate W caused by the vacuum 22 of the pimple table 20 compared tothe force on the substrate W at the edge in the vicinity of burls 348.The calculation must take the stiffness of the burls into account and ifthe burls are manufactured from a low expansion material such asZerodur, they should be about 80 nm less high than the burls of thepimple table 20. The gap between the portion 48 and the bottom of thesubstrate W is in an embodiment about 20 μm.

In the version of FIG. 7 b, portion 45 is similar in shape to that ofthe first version. However, an alternative has a ring or circularpattern of burls 345 positioned above portion 45. The discrete nature ofthe burls 345 allows gas from channel 42 to be sucked into thecompartment 44. These burls 345 are also about 80 nm less high than theburls of the pimple table 20. In an embodiment, gap D1 in between theburls 345 is about 50 μm. The burls 345 may be formed by the pimpletable 20 and need not necessarily be part of the substrate table WT.

From the above two versions of the third embodiment it will be clearthat the architecture of the gas seal formed by passages 42 and 47 canbe formed either completely by the substrate table WT, completely by thepimple table 20 or by a combination of both. FIGS. 7 c and 7 dillustrate two further versions of the third embodiment. FIG. 7 cillustrates a third version of the third embodiment in which the gasseal is formed by members of the pimple table 20. The portion 45 of thefirst and second versions is formed by a (annular) portion of the pimpletable 2045 and portion 48 of the first and second versions is formed by(annular) portion 2048 of the pimple table 20. Passages 2042, 2047equivalent to 42 and 47 are formed between the portions 20, 2045 and2048. However, only a part of the gas flow passes through the twopassages 2042, 2047; as illustrated, some gas flows under the pimpletable 20 which is effective to block further ingression of immersionliquid which seeps under the outer edge of the pimple table 20. Thisarrangement has an advantage that all of the accurate dimensions aremade in the pimple table 20 and the substrate table WT does not containany complex grooves.

In a fourth version of the third embodiment illustrated in FIG. 7 d, noinlet channel 42 is provided and gas flows from the pimple table 20 into(annular) port 47. This version has an advantage that a more stablepressure is experienced between the substrate W and the pimple table 20because the pimple table 20 does not need its own vacuum source.Furthermore, extra passage 2047 which is provided in the third versionis no longer necessary and only passage 2042 is used. Thus, a singlevacuum source is effective both to clear away leaking immersion fluid aswell as holding the substrate in place. A gas source maybe requiredunder the pimple table 20 (perhaps the more usual vacuum port in thesubstrate table under the pimple table can be used for this purpose) sothat a flow of gas outwards can be established.

It will be clear that various features of each of the versions of thethird embodiment can be combined so long as a flow of gas radiallyoutwardly from the centre of the pimple table towards the vacuum 46 isachieved.

Embodiment 4

A fourth embodiment is illustrated in FIGS. 8 and 9 and is the same orsimilar as the first embodiment except as described below.

This embodiment is described in relation to an edge seal member 117which is an integral part of the substrate table WT. However, thisembodiment is equally applicable to an edge seal member 17 which ismovable relative to the substrate table WT.

In a first version of this embodiment as illustrated in FIG. 8 a, afurther edge seal member 500 is used to bridge the gap between the edgeseal member 117 and the substrate W. The further edge seal member isaffixed to the edge seal member 117. The further edge seal member 500 isremovably attachable against the surface of the substrate W opposite theprimary surface. In this embodiment the further edge seal member 500 canbe a flexible edge seal member which is actuatable to contact the undersurface of the substrate W. When the flexible edge seal member 500 isdeactivated it falls away from the substrate under gravity. The way thismay be achieved is illustrated in FIG. 9 and is described below.

It is likely that the further edge seal member 500 will not prevent allof the immersion liquid from the liquid supply system from entering thespace under the substrate W and for this reason a port 46 connected to alow pressure source may be provided under the substrate W adjacent edgesof the edge seal member 117 and the substrate W in some or all of theversions of this embodiment. Of course the design of the area under thesubstrate could be the same as that of the third embodiment.

The same system can be used for sensors such as a transmission imagesensor (TIS) on the substrate table as opposed for the substrate W. Inthe case of sensors, as the sensors do not move, the edge seal member500 can be permanently attached to the sensor, for example using glue.

Furthermore, the edge seal member 500 can be arranged to engage with thetop surface of the object (that surface closest to the projection systemPL) rather than the bottom surface. Also, the further edge seal member500 may be provided attached to or near the top surface of the edge sealmember 117 as opposed to under the edge seal member 117 as isillustrated in FIG. 8 a.

A second version of this embodiment is illustrated in FIG. 8 b. Twofurther edge seal members 500 a, 500 b are used. The first of these edgeseal members 500 a is the same as in the first version. The second ofthese edge seal members 500 b is affixed to the substrate table 20 i.e.underneath the substrate W and extends with its free end radiallyoutwardly from its attachment point. The second further edge seal member500 b clamps the first further edge seal member 500 a against thesubstrate W. Compressed gas can be used to deform or move the secondfurther edge seal member 500 b.

A third version of this embodiment is shown in FIG. 8 c. The thirdversion is the same as the second version except the first further edgeseal member 500 c clamps the second further edge seal member 500 d tothe substrate W. This avoids, for example, the need for the compressedgas of the second version.

It will be appreciated that the embodiment will also work with only thesecond further edge seal member 500 b, 500 d with or without connectionto vacuum.

Various ways of deforming the further edge seal members 500, 500 a, 500b, 500 c, 500 d will now be described in relation to the first versionof the embodiment.

As can be seen from FIG. 9, a channel 510 is formed in the elongatedirection of a flexible further edge seal member 500 (which in anembodiment is an annular ring) and (a) discrete port(s) are provided inan upper surface of the flexible further edge seal member which facesthe projection system PL and the underside of the substrate W. Byconnecting a vacuum source 515 to the duct 510 the flexible further edgeseal member can be made to abut the substrate W by suction. When thevacuum source 515 is disconnected or switched off, the flexible furtheredge seal member 500 drops under gravity and/or pressure from port 46 toassume the position shown in dotted lines in FIG. 9.

In an alternative embodiment a flexible further edge seal member 500 isformed with a mechanical pre-load such that it contacts the substrate Wwhen the substrate is placed on the pimple table 20 and the flexiblefurther edge seal member 500 deforms elastically so that it applies aforce upwards on the substrate W to thereby make a seal.

In a further alternative, a flexible further edge seal member 500 maybeforced against the substrate W by an overpressure generated bypressurised gas on port 46.

A flexible further edge seal member 500 may be fashioned from anyflexible, radiation and immersion liquid resistant, non-contaminatingmaterial, for example, steel, glass e.g. Al₂O₃, ceramic material e.g.SiC, silicon, Teflon, low expansion glasses (e.g. Zerodur™ or ULE™),carbon fibre epoxy or quartz and is typically between 10 and 500 μmthick, in an embodiment between 30 and 200 μm or 50 to 150 μm in thecase of glass. With a flexible further edge seal member 500 of thismaterial and these dimensions, the typical pressure to be applied to theduct 510 is approximately 0.1 to 0.6 bar.

Embodiment 5

A fifth embodiment is illustrated in FIG. 10 and is the same or similaras the first embodiment except as described below.

This embodiment is described in relation to an edge seal member 117which is an integral part of the substrate table WT. However, thisembodiment is equally applicable to an edge seal member 17 which ismovable relative to the substrate table WT.

In the fifth embodiment, the gap between the edge seal member 117 andthe substrate W is filled with a further edge seal member 50. Thefurther edge seal member is a flexible further edge seal member 50 whichhas a top surface which is substantially co-planar with the primarysurfaces of the substrate W and the edge seal member 117. The flexiblefurther edge seal member 50 is made of a compliant material so thatminor variations in the diameter/width of substrate W and in thethickness of the substrate W can be accommodated by deflections of theflexible further edge seal member 50. When liquid in the liquid supplysystem under the projection system PL passes over the edge of thesubstrate, the liquid cannot escape between the substrate W, flexiblefurther edge seal member 50 and edge seal member 117 because the edgesof those elements are tight against one another. Furthermore, becausethe primary surfaces of the substrate W and the edge seal member 117 andthe top surface of the flexible further edge seal member 50 aresubstantially co-planar, the liquid supply system operation is not upsetwhen it passes over the edge of the substrate W so that disturbanceforces are not generated in the liquid supply system.

As can be seen from FIG. 10, the flexible further edge seal member 50isin contact with a surface of the substrate W opposite the primarysurface of the substrate W, at an edge portion. This contact has twofunctions. First the fluid seal between the flexible further edge sealmember 50 and the substrate W may be improved. Second, the flexiblefurther edge seal member 50 applies a force on the substrate W in adirection away from the pimple table 20. When the substrate W is held onthe substrate table WT by, e.g. vacuum suction, the substrate can beheld securely on the substrate table. However, when the vacuum source isswitched off or disconnected, the force produced by the flexible furtheredge seal member 50 on the substrate W is effective to push thesubstrate W off the substrate table WT thereby aiding loading andunloading of substrates W.

The flexible further edge seal member 50 is made of a radiation andimmersion liquid resistant material such as PTFE.

Embodiment 6

FIG. 11 illustrates a sixth embodiment which is the same or similar asthe first embodiment except as described below.

This embodiment is described in relation to an edge seal member 117which is an integral part of the substrate table WT. However, thisembodiment is equally applicable to an edge seal member 17 which ismovable relative to the substrate table WT.

The sixth embodiment illustrates how the pimple table 20 can bedecoupled from the liquid supply system between the substrate W and theedge seal member 117. This is done by positioning an opening exposed tothe atmosphere 65 between the edge of the substrate W and the vacuumholding the substrate W on the substrate table WT and associated withthe pimple table 20.

A layer 60, positioned on the opposite side of the substrate W to theprojection system PL and under the substrate at its edge leaving a gapbetween the substrate W and the layer 60 of about 10 μm, comprises anymaterial which is hydrophobic such as Teflon™, silicon rubber, or otherplastics material. Inorganic materials are desired because they havebetter radiation resistance. In this way, liquid which finds its wayinto the gap between the substrate W and the edge seal member 117 whenthe liquid supply system is positioned over the edge of the substrate Wis repelled such that an effective seal is formed and liquid does notfind its way to the pimple table 20. In an embodiment, the immersionliquid has a 0contact angle of at least 90° with the hydrophobic layer60.

Embodiment 7

A seventh embodiment will be described with reference to FIGS. 12 to 15.The seventh embodiment is the same or similar as the first embodimentexcept as described below.

In the seventh embodiment, as is illustrated in FIG. 12, the edge sealmember 17 is annular with a central hole larger than the diameter of thecircular substrate W. The shapes of the substrate W and edge seal member17 maybe different than annular so long as the central hole of the edgeseal member 17 is larger than the outer diameter/width of the substrateW. In this way, the edge seal member 17 may accommodate variations inthe substrate W diameter/width.

The edge seal member 17 is movable on the substrate table WT such thatwhen the liquid supply system moves towards an edge portion of thesubstrate W in order to expose it, the edge seal member 17 can be movedclosely to abut that edge portion of the substrate W which is to beexposed. This is best illustrated in FIG. 13 where the left hand side ofthe substrate W is about to be exposed.

As is clearly illustrated in FIG. 14, the edge seal member 17 is movableboth in the plane of the primary surface of the substrate W and in anembodiment also in the Z direction (i.e. in the direction of the opticalaxis of the apparatus). In this way, the edge seal member 17 can bemoved to the edge of the substrate W when required and can have theheight of its top (primary) surface adjusted so that its primary surfaceis closely co-planar with the primary surface of the substrate W. Thisallows the liquid supply system to effectively contain the immersionliquid in its reservoir even when the edge of the substrate W is beingimaged.

Also illustrated in FIG. 14 is a projection 175 which has a top surfacewhich is co-planar with the primary surface of the edge seal member 17,i.e. the primary surface of the edge seal member 17 overhangs on an edgeadjacent the substrate W so that the projection extends towards theoptical axis of the apparatus. As can be seen from FIG. 14, this allowsthe gap between the primary surfaces of the substrate W and edge sealmember 17 to be minimised even when the edge of the substrate W isslightly curved (i.e. the edge of the substrate W is not perpendicularto the primary surface).

Another way of improving or reducing the gap between the edge sealmember 17 and the substrate W is to provide a further (flexible) edgeseal member 177 between the edge of the edge seal member 17 closest tothe substrate W and the substrate W. This is illustrated in FIG. 15.This maybe done with or without a projection 175. A further flexibleedge seal member 177 can deform around the edge of the substrate W so asto form a tight seal with the substrate W. The further flexible edgeseal member 177 is attached to the edge seal member 17. The furtherflexible edge seal member 177 has an upper surface which issubstantially co-planar with the primary surfaces of the substrate W andthe edge seal member 17.

Embodiment 8

FIG. 16 illustrates an eighth embodiment which is the same or similar asthe first embodiment except as described below.

This embodiment is described in relation to an edge seal member 117which is an integral part of the substrate table WT. However, thisembodiment is equally applicable to an edge seal member 17 which ismovable relative to the substrate table WT.

As can be seen from FIG. 16, the eighth embodiment includes a furtheredge seal member 100 for bridging the gap between the edge seal member117 and the substrate W. In this case the further edge seal member 100is a gap seal member which is positioned on the primary surfaces of thesubstrate W and the edge seal member 117 to span the gap between thesubstrate W and edge seal member 117. Thus, if the substrate W iscircular, the gap seal member 100 will also be circular (annular).

The gap seal member 100 may be held in place by the application of avacuum 105 to its underside (that is a vacuum source exposed through avacuum port on the primary surface of the edge seal member 117). Theliquid supply system can pass over the edge of the substrate W withoutthe loss of liquid because the gap between the substrate W and the edgeseal member 117 is covered over by the gap seal member 100. The gap sealmember 100 can be put in place and removed by the substrate handler sothat standard substrates and substrate handling can be used.Alternatively, the gap seal member 100 can be kept at the projectionsystem PL and put in place and removed by appropriate mechanisms (e.g. asubstrate handling robot). The gap seal member 100 should be stiffenough to avoid deformation by the vacuum source. Advantageously the gapseal member 100 is less than 50, in an embodiment 30 or 20 or even 10 μmthick to avoid contact with the liquid supply system, but should be madeas thin as possible.

The gap seal member 100 is advantageously provided with tapered edges110 in which the thickness of the gap seal member 100 decreases towardsthe edges. This gradual transition to the full thickness of the gap sealmember ensures that disturbance of the liquid supply system is reducedwhen it passes on top of the gap seal member 100.

The same way of sealing may be used for other objects such as sensors,for example transmission image sensors. In this case, as the object isnot required to move, the gap seal member 100 can be glued in place (ateither end) with a glue which does not dissolve in the immersion liquid.The glue can alternatively be positioned at the junction of the edgeseal member 117, the object and the gap seal member 100.

Furthermore, the gap seal member 100 can be positioned underneath theobject and an overhang of the edge seal member 117. The object may beshaped with an overhang also, if necessary.

The gap seal member 100, whether above or below the object, can have apassage provided through it, from one opening in a surface in contactwith the edge seal member 117 to another opening in a surface in contactwith the object. By positioning one opening in fluid communication withvacuum 105, the gap seal member 100 can then be kept tightly in place.

Embodiment 9

A ninth embodiment will be described with reference to FIG. 17. Thesolution shown in FIG. 17 bypasses some of the problems associated withimaging edge portions of the substrate W as well as allows atransmission image sensor (TIS) 220 (or other sensor) to be illuminatedby the projection system PL under the same conditions as the substrateW.

The ninth embodiment uses the liquid supply system described withrespect to the first embodiment. However, rather than confirming theimmersion liquid in the liquid supply system under the projection systemPL on its lower side with the substrate W, the liquid is confined by anintermediary plate 210 which is positioned between the liquid supplysystem and the substrate W. The spaces 222, 215 between the intermediaryplate 210 and the TIS 220 and the substrate W are also filled withliquid 111. This may either be done by two separate space liquid supplysystems via respective ports 230, 240 as illustrated or by the samespace liquid supply system via ports 230, 240. Thus the space 215between the substrate W and the intermediary plate 210 and the space 222between the transmission image sensor 220 and the intermediary plate 210are both filled with liquid and both the substrate W and thetransmission image sensor can be illuminated under the same conditions.Portions 200 provide a support surface or surfaces for the intermediaryplate 210 which may be held in place by vacuum sources.

The intermediary plate 210 is made of such a size that it covers all ofthe substrate W as well as the transmission image sensor 220. Therefore,no edges need to be traversed by the liquid supply system even when theedge of the substrate W is imaged or when the transmission image sensoris positioned under the projection system PL. The top surface of thetransmission image sensor 220 and the substrate W are substantiallyco-planar.

The intermediate plate 210 can be removable. It can, for example, be putin place and removed by a substrate handling robot or other appropriatemechanism.

Embodiment 10

FIG. 18 shows a modification of the liquid supply system which isapplicable to any other embodiment described herein which is effectiveto increase the size of gap the immersion liquid can span before suddenliquid loss.

A plurality of capillaries 600 are provided between the liquid supplysystem (e.g. seal member 12) and the projection system PL. Thesecapillaries extend generally upwardly, i.e. away from the substrate W.If the capillaries have a radius r, the liquid film thickness h, whichcan be supported by the capillary, is given by the formula:

$h = \frac{2\sigma\;\cos\;\theta}{{rg}\;\rho}$

where a is the interfacial tension, θ the contact angle between theliquid and the capillaries W and ρ the liquid density. Thus by makingcos θ positive (i.e. making the inner surface of the capillarieshydrophobic, for example by a coating) the capillaries can support aportion of liquid with height h above the gap so that a larger gap canbe spanned.

By applying a voltage between the hydrophobic coated capillaries and theliquid, cos θ can be reduced to around zero and this allows free flow ofliquid through the capillaries 600 (according to equation 1 above) sothat liquid can be removed from the liquid supply system under theprojection system PL in little time by keeping the length of thecapillaries low. This is advantageous for keeping the liquid clean. Whenthe edge of the substrate W is imaged, the voltage can be removed sothat the gap can be spanned. In order to lift the liquid film from thesubstrate W, it is proposed to coat the substrate W edges with ahydrophobic material (or the resist on the substrate W edges can beremoved as the substrate material itself is hydrophobic).

The capillaries 600 may be provided by substantially straight ducts witha substantially circular cross-section or by other shaped ducts. Forexample, the capillaries may be made up of voids in a porous material.

Embodiment 11

FIG. 19 shows an eleventh embodiment which is the same as the firstembodiment except as described below.

In the eleventh embodiment the object on the substrate table WT is asensor 220 such as a transmission image sensor (TIS). In order toprevent immersion liquid seeping underneath the sensor 220, a bead ofglue 700 which is undissolvable and unreactable with the immersion fluidis positioned between the edge seal member 117 and the sensor 220. Theglue is covered by immersion fluid in use.

Embodiment 12

A twelfth embodiment is described with reference to FIGS. 20 and 21. Inthe twelfth embodiment it is a sensor 220 which is being sealed to thesubstrate table WT. In both versions illustrated in FIGS. 20 and 21, avacuum 46 is provided adjacent the gap with an opening passage 47 and achamber 44 for taking away any immersion liquid which should find itsway through the gap between the edge seal member 117 and the edge of thesensor 220.

In the FIG. 20 version, the vacuum 46 is provided in the substrate tableWT under an overhang portion of the object 220. The passage 47 isprovided in an overhanging inwardly protruding portion of the substratetable WT. Optionally a bead of glue 700 is positioned at the inner mostedge of the protruding portion between the substrate table WT and theobject 220. If no bead of glue 700 is provided, a flow of gas fromunderneath the object 220 helps seal the gap between the sensor 220 andthe substrate table WT.

In the version of FIG. 21, the vacuum 46, compartment 44 and passage 47are provided in the object 220 itself under an inwardly protruding edgeseal member 117. Again there is the option of providing a bead of gluebetween the object 220 and the substrate table WT radially outwardly ofthe passage 47.

All of the above described embodiments maybe used to seal around theedge of the substrate W. Other objects on the substrate table WT mayalso need to be sealed in a similar way, such as sensors includingsensors and/or marks which are illuminated with the projection beamthrough the liquid such as a transmission image sensor, an integratedlens interferometer and scanner (wavefront sensor) and spot sensorplates. Such objects may also include sensors and/or marks which areilluminated with non-projection radiation beams such as levelling andalignment sensors and/or marks. The liquid supply system may supplyliquid to cover all of the object in such a case. Any of the aboveembodiments may be used for this purpose. In some instances, the objectwill not need to be removed from the substrate table WT as, in contrastto the substrate W, the sensors do not need to be removed from thesubstrate table WT. In such a case the above embodiments maybe modifiedas appropriate (e.g. the seals may not need to be moveable).

Each of the embodiments may be combined with one or more of the otherembodiments as appropriate. Further, each of the embodiments (and anyappropriate combination of embodiments) can be applied simply to theliquid supply system of FIG. 2 and FIGS. 19 and 20 without the edge sealmember 17, 117 as feasible and/or appropriate.

The shape of the edge seal member 117 and the top outer most edge of thesensor 220 can be varied. For example, it may be advantageous to providean overhanging edge seal member 117 or indeed an outer edge of thesensor 220 which is overhanging. Alternatively, an outer upper corner ofthe sensor 220 may be useful.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. In particular, the invention is also applicable toother types of liquid supply systems, especially localized liquid areasystems. If the seal member solution is used, it maybe one in which aseal other than a gas seal is used. The description is not intended tolimit the invention.

1. A lithographic projection apparatus comprising: a support structureconfigured to hold a patterning device, the patterning device configuredto pattern a beam of radiation according to a desired pattern; aprojection system configured to project the patterned beam onto a targetportion of a substrate; a substrate table configured to hold thesubstrate, said substrate table comprising: an edge seal memberconfigured to at least partly surround an edge of at least one of saidsubstrate and an object positioned on said substrate table, and afurther edge seal member configured to extend across the gap betweensaid edge seal member and said at least one of said substrate and saidobject and to be in contact with said at least one of said substrate andsaid object; and a liquid supply system configured to provide a liquid,through which said beam is to be projected, in a space between saidprojection system and said at least one of said substrate and saidobject, wherein said further edge seal member is flexible.
 2. Anapparatus according to claim 1, wherein said flexible further edge sealmember is attached to said edge seal member.
 3. An apparatus accordingto claim 1, wherein said flexible further edge seal member has a port,connected to a vacuum source, adjacent its end distal from said edgeseal member, such that on actuation of said vacuum source, said flexiblefurther edge seal member is deflectable upwards to contact against saidat least one of said substrate and said object to form a seal betweensaid flexible further edge seal member and said at least one of saidsubstrate and said object due to the force generated by the vacuumsource acting on said at least one of said substrate and said object. 4.An apparatus according to claim 1, further comprising a second flexiblefurther edge seal member attached under said at least one of saidsubstrate and said object to said substrate table and with a free endradially outwardly from the attachment point.
 5. An apparatus accordingto claim 1, wherein said flexible further edge seal member is disposedbetween said edge seal member and said at least one of said substrateand said object and with a surface substantially co-planar with saidprimary surfaces of said edge seal member and said at least one of saidsubstrate and said object.
 6. An apparatus according to claim 5, whereinsaid flexible further edge seal member is shaped to contact said atleast one of said substrate and said object on a surface opposite itsprimary surface.
 7. An apparatus according to claim 5, wherein saidflexible further edge seal member is effective to apply a force to saidat least one of said substrate and said object away from said substratetable when said at least one of said substrate and said object is heldon said substrate table.
 8. An apparatus according to claim 1, whereinsaid object comprises a sensor.
 9. An apparatus according to claim 1,wherein at least one said edge seal member and further edge seal memberis glued to said at least one of said substrate and said object around aperiphery of said at least one of said substrate and said object.